The use of delivery devices employing catheters have long been known and used for a variety of medical procedures for establishing, re-establishing or maintaining passages, cavities or lumens in vessels, organs or ducts in human and veterinary patients. For these procedures, it has also long been known to deliver an implant by means of a catheter, often intraluminally. For example, a stent, stent-graft, filter or occlusion device may be delivered intraluminally from the femoral artery for deployment.
For procedures which implant into the patient a prosthesis or other device, the device to be implanted is normally held onto the catheter in a compressed state and then released from the catheter so as to expand to its normal operating state, prior to withdrawal of the catheter from the patient to leave the implant in position.
A variety of delivery mechanisms are known in the art. These generally involve positioning the implant on a distal part of the delivery device, that is at an end furthest from the external manipulation end used by the clinician during the deployment procedure. The prosthesis or implant is normally held to the distal end of the catheter by a suitable restraining mechanism, such as restraining wires or the like. It is also conventional to cover the implant with a sheath in order to protect the implant and also the patient's lumens or organs during the delivery process. Once the implant has been positioned at the location in which it is to be released, the sheath is removed to expose the implant. This is then expanded, either automatically if the implant is of the self-expanding type or by a suitable expanding mechanism if not, such as by means of an expansion balloon.
In cases where a sheath or other covering is provided, some delivery devices include a mechanism by which the sheath can be withdrawn by being pulled back towards the external manipulation end of the delivery device, that is towards the surgeon or other clinician. For this purpose, the delivery device typically includes a pusher member held within the outer sheath and to which an opposing force can be applied during the action of pulling the sheath back. Delivery apparatus of this type is well known, for example for the delivery of stents and stent-grafts, particularly to the aorta.
In other instances it is desirable to have a device which does not require retraction or withdrawal of the containment sheath prior to expansion of the implant. This may be, for example, in cases where the device and the implant have a small outer diameter, in which case the components of the delivery device are desirably as small and as thin as possible whilst maintaining their ability to provide the required delivery function.
In such instances, the containment sheath may be of a type which can be split open so as to allow expansion of the implant from its contracted state. The containment sheath, in this example could be withdrawn from the patient but is often left within the patient, trapped between the expanded implant and the internal walls of the patient's lumen or organ. In such a case, the material forming the sheath may be of a biodegradable or bioabsorbable material.
WO-98/20812 discloses a series of examples of sleeve splitting mechanisms for splitting the containment sleeve or sheath provided to protect an implant during deployment. In some of the examples described, the sleeve is provided with a plurality of weakening points which tear upon expansion of a balloon used for expanding the stent, stent-graft or other implant held on the catheter. Other examples provide for a cutting wire to cut through the sleeve and hence to release the implant held therewithin.
An arrangement using a cutting wire is also disclosed in EP-A-1,200,017, U.S. Pat. Nos. 6,576,005 and 6,183,481.
WO-99/47074 discloses another arrangement, in which in place of a sleeve there is provided a thread which is wound around the stent held on the catheter and which is then unwound so as to release the stent.